In the past, many tools have been devised for boring or drilling holes in workpieces, particularly for use in the field of woodworking. Such tools are most often used in hand drills, electric drills, drill presses, lathes, and the like. Such implements range from the conventional drill bits of the so-called "twist" type, to the "spade" type bits often used for larger diameter holes, to fly cutters which are often used for cutting still larger holes into the workpiece.
The twist type drill bits usually include a pair of cutting edges machined on the leading face of the bit and formed in such a manner that the edges meet at a point and connect to spiral grooves formed in the body of the bit.
The spade type bits, as their name implies, has a flat body portion and a pair of cutting edges formed at the leading edge of the body and connected by a point which extends in the advancing direction of the bit.
Fly cutters typically have a radially directed arm to which is attached a small twist type drill bit, used to center the cutter, and a parallel blade extending forwardly of the arm with a cutting edge on the distal edge of the blade. The blade rotates about the drill bit, and the tool cuts an annular plug out of the workpiece, rather than cutting all of the material within the outer diameter of the tool as in the case of other types of bits.
Each of these types of implements, however, suffers from the disadvantage that they cannot be used for increasing the size of a previously drilled or bored hole in a workpiece. These prior art implements lack this specific ability since they each rely upon a centering point about which the cutting edges rotate, but for a pre-existing hole, there is no material which this point can engage, and thus there is no way to center the tool.
In essence, the prior art lacks the ability to increase the diameter of an existing hole while reliably maintaining the original center.
This disadvantage is not quite as significant in the case of a twist drill, since the tapered cutting edges tend to self-center on the pre-existing hole, but this method lacks the precision required by many craftsmen.
In addition, the twist drills, because of their tapered point, cannot drill a hole with a flat bottom, nor can they drill a stepped hole with a squared off shoulder as is often necessary in wooden joint construction.
Although some of these problems can be overcome with a lathe using a cutting tool, this requires a rather significant expense to accomplish a rather simple job.
In the past, some tools have been proposed for overcoming these disadvantages, such as the counterboring tool described in U.S. Pat. No. 2,009,168 issued July 23, 1935 to A. B. Dettmer. However, this device has apparently met with little success as the same problems continue to face the craftsman.
Therefor, a primary object of the present invention is to provide an improved tool for enlarging the diameter of pre-existing holes.
Another object of this invention is to provide a tool which may be used in hand drills, portable electric drills, drill presses, or lathes with equal success.
A further object of this invention is to provide an improved hole sizing tool wherein a particular cutting member may be used with different size pilot members or a particular pilot member may be used with different size cutting members.
Still another object of the present invention is to provide an improved hole sizing tool capable of enlarging existing holes while reliably maintaining the original center of the hole.
Yet another object of the invention is to provide an improved hole sizing tool which can provide hole having a flat bottom.
Yet a further object of this invention is to provide a hole sizing tool which can be used to enlarge the size of holes and be capable of use with fractional horsepower motors of the type normally encountered in portable electric drills.
Still another object of this invention is to provide a hole sizing tool which is capable of making smooth cuts in wood, plastic, or other "soft" materials and keeping the sides of the enlarged hole parallel to the pre-existing hole.
These and other objects and advantages of this invention will become apparent when considered in light of the description and claims when taken together with the accompanying drawings.